The present invention generally relates to electrophotography and more particularly, to a developing apparatus for use in an image forming apparatus such as an electrophotographic copying apparatus or the like.
Conventionally, as one example of a developing apparatus of the type referred to above, there has been proposed, for example, in U.S. Pat. No. 4,615,606, an arrangement as shown in FIG. 5 which includes a developing sleeve S disposed adjacent to an electrostatic latent image support member or a photoreceptor drum 1, a magnet roller M having a plurality of magnets with magnetic poles extending in an axial direction and defined adjacent one another in a circumferential direction, and incorporated within said developing sleeve S, a toner supply roller T formed on its surface with very small recesses (not shown) and confronting the peripheral surface of said developing sleeve S with a predetermined gap defined therebetween and a toner accommodating portion H located above or at a side portion of said toner supply roller T.
In the above-described developing apparatus, the developing material held on the surface of the developing sleeve S forms a magnetic brush along magnetic lines of force of the magnets provided on the magnet roller M so as to form a toner image on the surface 1a of the electrostatic latent image support member or photoreceptor drum 1 after rubbing against said surface.
Between the developing sleeve S and the supply roller T, there is impressed a potential difference, by which toner corresponding to the consumption thereof is replenished to the developing sleeve S.
In the above-described known developing apparatus, however, situations arise in which the toner falls from the very small recesses due to centrifugal force or vibrations, etc. based on the rotation of the toner supply roller T, and accumulate on the roller end portions between the developing sleeve S and the toner supply roller T.
Thus, problems are present in which, for example, during withdrawal of the developing sleeve S for maintenance work or the like, the toner accumulated as described above is disturbed or diffused in the direction of width of the developing sleeve S, consequently casing toner to scatter from the developing apparatus to soil neighboring appliances. Also, because the toner mixing ratio becomes extremely high at the opposite end portions of the developing sleeve S, if said sleeve S is mounted in a state in which the toner is disturbed, undesirable fogging, specks and the like are formed in the copied images, thus resulting in a deteriorated image quality.
Furthermore, when a toner supply width of the supply roller T is larger than an effective magnetic brush width on the developing sleeve S, because a blade P is held in contact with the toner supply roller T so as to restrict the amount of toner passing thereby, the toner disposed at the end portions of the supply roller T and not contacting the magnetic brush as described above tends to aggregate and solidify on the blade P due to the contact therewith over a long period of time. When such aggregated and solidifed toner is finally transferred onto the developing sleeve S, a gap between the developing sleeve S and a magnetic brush bristle height restricting plate (not shown) is clogged by such toner, thus preventing a smooth transport of the developing material.